In the preceding grant periods the mechanisms of electroacupuncture (EA) analgesia were studied in normal healthy animals without pain problems. This is obviously an arbitrary situation quite different from the clinical practice where the patients are under acute or chronic pain. In the present study we intend to observe EA analgesia in animals under chronic pain, with emphasis being put on the cumulative effect induced by multiple EA treatments, and to explore whether genetic factors are involved in determining the effectiveness of EA analgesia. Chronic pain models include mono-arthritis induced by local injection of kaolin/carrageenin, or of Freund's complete adjuvant, and muscle spasticity/pain induced by spinal cord constriction. Best parameters of EA, and the optimal intervals of multiple EA treatments (30 min per session) will be worked out, and the hypothesis will be tested whether a gradual increase of the therapeutic effect is accounted for by the increased induction of the expression of the opioid genes in the CNS. The second aim is to test the hypothesis that the efficacy of EA analgesia can be manipulated by tilting the balance between the expression of two sets of genes encoding the opioid peptides vs the antiopioid peptide cholecystokinin (CCK). Antisense oligonucleotide or cDNA will be transferred intracerebrally or intrathecally to produce a selective suppression of the opioid gene or CCK gene, and its effect on EA analgesia is monitored. The third aim is based on the finding that continuous EA for 6-10 hours leads to a decrease or abolishment of its analgesic effect. Since EA of different frequencies has been shown to release different opioid peptides (low frequency EA releases enkephalins to interact with mu/delta opioid receptors and high frequency EA releases dynorphins to interact with kappa opioid receptors), we thought to test whether a prolonged and profound release of opioid peptides induced by continuous EA stimulation leads to a down regulation and decreased gene expression of the corresponding opioid receptor protein. In summary, this project tries to study the mechanisms of EA analgesia in two directions: close to the clinical practice, and deep to the molecular level. Once it is clear that peripheral electrical stimulation of identified parameters (frequency, intensity, duration, etc.) will lead to an augmentation of the biosynthesis and release of our "natural pain killers", why not use them to replace, or at least to reduce, the use of pain killers, and help to lower the cost for chronic pain treatment.